This invention relates to magnets and, more particularly, but not exclusively, to iron-rare earth-boron or iron-cobalt-rare earth-boron type magnets, and a method of production thereof. Iron-rare earth-boron and iron-cobalt-rare earth-boron type magnets are disclosed in U.S. Pat. No. 4,601,875, and European Patents EP-A-0101552 and EP-A-0106948. In particular, U.S. Pat. No. 4,601,875 and EP-A-0101552 disclose the production of permanent magnets based on the Fe.B.R system wherein R is at least one element selected from light-and heavy-rare earth elements inclusive of yttrium (Nd, Pr, La, Ce, Tb, Dy, Ho, Er, Eu, Sm, Gd, Tm, Yb, Lu and Y) and wherein the B content is 2 to 28 atomic percent, the R content is 8 to 30 atomic percent and the balance is iron. Such a permanent magnet is produced by providing a sintered body of the alloy. U.S. Pat. No. 4,601,875 requires the sintered body to be heat treated (or aged) at 350.degree. C. to the sintering temperature for 5 minutes to 40 hours in a non-oxidizing atmosphere. The aging process is believed to promote growth of a grain boundary phase which imparts coercivity. U.S. Pat. No. 4,601,875 also discloses alloys in which cobalt can be substituted for iron in an amount not exceeding 45 atomic percent of the sintered body. Additionally, U.S. Pat. No. 4,601,875, EP-A-0101552 and EP-A-0106948 disclose the possibility of including at least one of additional elements M in certain specified maximum amounts, M being selected from Ti, Ni, Bi, V, Nb, Ta, Cr, Mo, W, Mn, Al, Sb, Ge, Sn, Zr and Hf.
However, the above processes are relatively expensive in that they involve having to sinter at an elevated temperature and then age the sintered body.
Additionally, sintering has an affect on the particle size in the sintered body and so it is not always possible to optimize the particle size, with the result that the magnetic properties can suffer. Also, sintered magnets are difficult to machine.
With alloys based on the Fe.B.R system, the grain boundary phase, which is always present in the non-stoichiometric alloys, is very susceptible to oxidation, with the result that such alloys are very difficult to use in the manufacture of polymer bonded magnets and also have to be protected to prevent corrosion in service.